This invention relates generally to well pumping units and more specifically to a simplified and improved drive for imparting reciprocating movement to the polish rod of the pump. The invention includes an improved and reliable reversing mechanism which provides a dwell period between an upstroke and a downstroke wherein the power source is in an off position. The dwell period may be easily adjusted to suit design and field conditions. Thus, the usual shock experienced during stroke exchange from an upstroke to a downstroke is cushioned to thereby reduce wear and tear on parts and increase the life of the unit. Additional cushioning is provided by a winding drum structure which slows reciprocation of the unit, at the point of exchange from a downstroke to an upstroke.
The invention has particular utility with a long stroke, well pump employing an electric motor as the power source. I have developed such a well pumping unit, as herein disclosed, which includes a tower mounted on a base platform, a source of power in the form of an electric motor, a winding drum on the base platform driven from the electric motor, and a lift belt made of conveyor belting from the winding drum up to the top of the tower and over a spool mounted thereon and then extended downwardly and secured to the polish rod of the otherwise conventional well pump. A counterbalance or counterweight is attached to that portion of the drive belt between the spool and the winding drum so that power requirements are kept to a minimum. An idler spool is provided in the tower and that portion of the lift belt between the counterweight and the winding drum is trained beneath the idler pulley or spool so as to eliminate any side to side movement of the counterweight during operation of the pump. The reversing mechanism and winding drum are arranged and configured to minimize the shock of exchange between an upstroke and a downstroke, at which time the power source for the winding drum reverses direction, and between a downstroke and an upstroke, at which time the lift belt is rewound upon the drum, respectively.
A brief description of the background of development of well pumping units is appropriate. In the early life of a well, reservoir pressure alone may be sufficient to lift the oil to the surface, providing local regulatory authorities permit such a procedure. However, such pressure is eventually exhausted whereupon the oil must be pumped to the surface. The most common variety of pump in use is a walking beam pump having a nominal stroke of approximately seven to 10 feet. A walking beam pump is suitable for shallow wells, but such a pump becomes inefficient and eventually inoperable with wells which are one, two or miles deep. Specifically, rod stretch may become equal to stroke distance, thus rendering a walking beam pump completely inoperable when used with a very deep well.
Thus, long stroke, well pumping units particularly useful in deep wells, have been developed, some having stroke lengths of thirty-two feet or more. An example of such a prior art long stroke pumping unit is the "Oilwell" Long Stroke Pumping Unit, made by Oilwell, a division of United States Steel. The unit includes a central tower having multiple guides to stabilize the structure, a complex multi-strand cable crown block assembly suspending the rod string, a variable capacity counterweight, and a prime mover. A wire line drum is used having a helix track operative during exchange from a downstroke to an upstroke to slow wire line travel somewhat, increase mechanical advantage on the well side of the pump, and thus reduce the shock of stroke reversal somewhat. This unit is both complex and expensive.
An improved wire line deep well pumping apparatus is disclosed and claimed in my own prior U.S. Pat. No. 3,248,958. A basic yo-yo variety of long stroke pumping unit discussed therein has a power system in which a cycle of windup (during pump upstroke) and payout (during pump downstroke) is accomplished without need for winding drum reversal; thus, the power source of the unit is reversed only after a full cycle of operation rather than with each stroke, as in prior art long stroke pumping units. As disclosed in this patent, an electric motor is used as the power source and during a downstroke, the winding drums work with the motor and thus a counter electromotive force is generated in the motor which can be employed to salvage much of the kinetic energy in the moving parts of the system. A simple limit switch is disclosed for reversing the electric motor; the patent further states that polish rod stroke and time delay may be modulated but discloses no structure or system for accomplishing such results. Another of my prior U.S. patents, U.S. Pat. No. 3,345,950 discloses a long stroke, deep well pumping unit either electrically or hydraulically powered and including a limit switch system alternately operated by the yoke suspending the polish rod and the counterweight to effect power source reversal.
Other long stroke, deep well pumping units that I have invented are disclosed in my prior U.S. Pat. Nos. 3,483,828; 3,538,777; 3,777,491; 3,792,836; and 3,986,564. FIGS. 4 and 5 of U.S. Pat. No. 3,777,491 disclose a hydraulically operated deep well pumping unit having a single, wide strap or belt as the operative connection between the polish rod and winding drum of the pump, which is somewhat similar to the lift belt of this invention.
However, the prior art does not disclose a simplified, uncomplicated long stroke, well pumping unit wherein a yo-yo drive as above discussed is employed with a flexible lift belt being the operative connection between the winding drum and the polish rod, power source reversal being positively associated with the winding drum rather than other components of the system, and stroke reversal being cushioned so as to reduce wear and tear on the unit and extend the life of the components of the unit. Of course, this unit is useful in wells of all depths, which particularly enhances the universality of application of the invention.